1. Field of the Invention
The present invention relates to an inverted pendulum type omnidirectional vehicle.
Priority is claimed on Japanese Patent Application No. 2009-217791, filed on Sep. 18, 2009, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, omnidirectional type carts such as described in, for example, Japanese Unexamined Patent Application, First Publication No. 2004-344435 have been proposed. Specifically, this cart includes: four wheels, each made of a Mecanum wheel; drive mechanisms that rotate each of the wheels about a wheel shaft thereof; a control apparatus that controls the drive mechanisms; and a vehicle body to which a plurality of wheels are attached and which receives the load of a passenger. The wheels (Mecanum wheels) each include: a rotation member that is disposed substantially vertical to a road surface and that is rotatable about a wheel shaft; and a plurality of free rollers that are evenly disposed around the outer circumference of the rotation member. The plurality of free rollers are rotatable about an axis (an axis of rotation) which intersects that of the wheel shaft at 45 degree angle. Each of them is brought into contact with the road surface when it is moved to the lowest end of the rotation member with the rotation of the rotation member. The drive mechanisms are made of motors, each of which is provided on the wheel shaft of each wheel. The control apparatus independently controls the rotation angles of the motors based on a detection result from a sensor that detects an external force acting on the vehicle body. According to a cart with the above structure, through control of the rotation angles of the motors by the control apparatus, the cart can be moved in a desired direction at a desired speed.
On the other hand, there is conventionally offered an inverted pendulum type vehicle that is steerable through an instinctive operation by a passenger shifting his or her weight. This vehicle includes: a pair of wheels disposed in parallel in the left-right direction; a drive mechanism that independently rotates the pair of wheels; a control apparatus that controls the drive mechanism; and a vehicle body to which the pair of wheel are attached. According to the vehicle, through control of the drive mechanism by the control apparatus according to the weight shift of the passenger on the vehicle, the pair of wheels are independently rotated, to thereby perform a forward-rearward movement, a change of direction, and an adjustment of speed.
In recent years, an inverted pendulum type omnidirectional vehicle in which the above-mentioned inverted pendulum type vehicle is combined with the above-mentioned Mecanum wheels has been under development.
However, if the aforementioned Mecanum wheels are used as wheels of an inverted pendulum type vehicle, there is a possibility that the direction of movement changes when a wheel on one side spins while traveling due to a rough road surface, leading to a problem with steering stability and ride quality while traveling. Especially, in the case of a vehicle in which an auxiliary wheel is disposed rearwardly of a pair of wheels, and free rollers provided on the wheels on both sides are arranged in the orientations such that the distance between the axes of rotation of the free rollers is gradually wider, when the free rollers are brought into contact with the ground, toward the auxiliary wheel (toward the rearward direction), a vertical distance from the ground contact point of the auxiliary wheel to an extension line of each axis of rotation (axis of rotation of each free roller in contact with the road surface) is long. Therefore, when the wheel on a first side spins while traveling, the moment acting on the wheel on a second side is large, making it likely to cause the vehicle to turn around with the auxiliary wheel as a pivot.
Furthermore, in the case where the free rollers on the wheels on both sides are arranged in the orientations described above, a lateral force with a vector diagonally forward on a first side acts only on the wheel on a second side if the wheel on the first side spins while moving forward, thus causing the vehicle to turn around on the first side. At this time, a load on the wheel on the first side (a spinning side) is reduced by the centrifugal force. This makes it difficult for the wheel on the first side to be restored from the spinning state.
In view of the aforementioned conventional problems, the present invention has an object to provide an inverted pendulum type omnidirectional vehicle capable of achieving high steering stability and excellent ride quality.